Scientists know plenty about depression. Now they are starting to understand the roots of positive emotion

Richard Davidson was in a lab observing a Buddhist Monk Sink deep into serene meditation when he noticed something that sent his own pulse racing. Davidson, a professor of psychology and psychiatry at the University of Wisconsin, hurriedly double-checked the data streaming to his computer from electrodes attached to the monk's skull, but there was no mistake. Electrical activity in the left prefrontal lobe of the monk's brain was shooting up at a tremendous rate. "It was exciting," Davidson recalls. "We didn't expect to see anything quite that dramatic."

Davidson's excitement is all the more significant because he's known by colleagues as the king of happiness research. When he made the discovery five years ago, he had been studying the link between prefrontal-lobe activity and the sort of bliss deep meditators experience. But even for someone with his experience, watching the brain crackle with activity as a person entered a trancelike state was unprecedented. It made clear, says Davidson, who published the research study in the Proceedings of the National Academy of Sciences last fall, that happiness isn't just a vague, ineffable feeling; it's a physical state of the brain--one that you can induce deliberately.

That's not all. As researchers have gained an understanding of the physical characteristics of a happy brain, they have come to see that those traits

have a powerful influence on the rest of the body. People who rate in the upper reaches of happiness on psychological tests develop about 50% more antibodies than average in response to flu vaccines, and that, says Davidson, "is a very large difference." Others have discovered that happiness or related mental states like hopefulness, optimism and contentment appear to reduce the risk or limit the severity of cardiovascular disease, pulmonary disease, diabetes, hypertension, colds and upper-respiratory infections as well. According to a Dutch study of elderly patients published in November, those upbeat mental states reduced an individual's risk of death 50% over the study's nine-year duration. Says Laura Kubzansky, a health psychologist at Harvard's School of Public Health, in a masterpiece of understatement: "There's clearly some kind of effect."

It makes sense that there should be. Doctors have known for years that clinical depression--the extreme opposite of happiness--can worsen heart disease, diabetes and a host of other illnesses. But the neurochemistry of depression is much better known than that of happiness, mostly because the former has been studied more intensively and for much longer. Until about a decade ago, says Dacher Keltner, a psychologist at the University of California, Berkeley, "90% of emotion research focused on the negative, so there still are all of these interesting questions about the positive state."